The effects of external noise on lifetime of metastable oscillation mode observed in forced van der Pol oscillator are investigated to clarify the origin of destablization of the modes. The noise is found to suppress the stability of the mode when the noise is intense enough compared with the fluctuation inherent to the oscillator.

Let G be a simple graph and α be an automorphism of G. A spanning tree T of G is said to be α-invariant if α is also an automorphism of T. We give a necessary and sufficient condition for a connected graph G to have an α-invariant spanning tree.

It is reported firstly that spatial filtering of laser beam by a receiving optical system such as a finite-aperture detector causes harmonic distortions of a directly modulated semiconductor laser diode when the beam irradiance is reflected partially at the submount. The theory based on geometrical optics for interference of directly emerging light and reflected light is developed and the numerical results are presented for a variety of laser structures and FM-modulation parameters.

The self-mixing type laser Doppler velocimter gives a simple method of directional velocimetry. The beat signal comprises the fundamental Doppler frequency as well as its harmonics, so that the waveform is like a sawtooth in which the sign of inclination reverses as the target changes the direction of its movement.

A test for detection of functions that are in the same equivalence class under permutations and negations of variables and negation of output with a totally symmetric function based on spectral methods is presented. These functions have essentially identical circuit realizations as corresponding totally symmetric functions which gives significance of this detection.

This paper investigates convergence properties of a circuit simulation technique called Waveform Relaxation (WR). A general formulation of a family of WR algorithms called a generalized WR is introduced. This formulation reduces to some hitherto introduced WR algorithms in particular cases. The following two sufficient conditions for the generalized WR method to converge locally are given: ) the capacitance matrix of the circuit is block strictly diagonally dominant and a time-steplength is sufficiently small; ) the conductance matrix of the circuit has the same property and a time-steplength is sufficiently large.

Determination of spare quantity assuming a general failure distribution is discussed. A new method is presented which is an extension of a usual normal approximation method. The original method is essentially a Normal distribution approximation" to a Poisson process of failure occurrence. On the other hand, the new method assumes a general failure distribution. The mean and the variance of the number of failures within for a given period of time are necessary for determining the spare quantity. The mean is obtained in a simple form. The variance is give as a solution of an integral equation. The solution of this equation for a general case is obtained by applying a discrete approximation technique. Some numerical examples are provided to discuss the difference between when assuming a general failure distribution and when assuming the exponential failure distribution.

Sea ice clutter was measured using an X-band radar which is located at the city of Mombetsu in Hokkaido. The pulsewidth of the radar was 80 nsec. To sample by 40 nsec and record digitally, an emitter coupled logic (ECL) was used as a high-speed IC. The sampled data were first transferred to 64 Kbyte dynamic memory board and next to a 5 inch floppy disk through an 8 bit micro-computer. These data were processed by a 16 bit micro-computer. As a result, it is shown that the amplitude of sea ice obeys a Weibull disturibution with shape parameters of c0.50 to 1.65. Thus, the amplitude statistics deviate from the well-known Rayleigh distribution of c2.0, in which a logarithmic/constant false alarm rate (LOG/CFAR) circuit is useful. Therefore, it is concluded that the new Weibull/CFAR should be considered to suppress sea ice clutter.

Fabrication of GaInAsP/InP heterostructure lasers for 1.5 µm wavelength region by organometallic vapor phase epitaxy are discussed. Results of growth conditions, which were experimentally found important to obtain the low threshold current density (1 kA/cm²) comparable with LPE at 1.5 µm lasing oscillation are reported, such as gas switching at hetero-interfaces, maintenance of constant temperature over the growth of all layers, selection of carrier gas and doping conditions. Furthermore, OMVPE device techniques for buried heterostructure laser operating at CW condition are described. Fabrications and characterization of quantum well structure are also reported.

The single fundamental transverse mode condition, both in three-layer DH, and asymmetrical five-layer separate confinement heterostructure (SCH) laser diodes operating at 1.55 µm wavelength, has been investigated based on the effective refractive index. The simple derived formula can be applied to obtain the effective refractive index of the dominant mode in DFB laser diodes to determine the corrugation period corresponding to the designed wavelength.

A novel measuring system on the amplitude and phase of the RF magnetic field is proposed. It is composed of a laser diode (LD) linked with a small loop antenna, an optical fiber transmission line, and phase-sensitive detection instruments. The LD output light is directly intensity-modulated by the RF current induced in the loop antenna by the RF magnetic field under test. The instantaneous amplitude and phase of the RF magnetic field are preserved in the modulated light because of the quick response of LD and are detected by the remote detection system. The characteristics of the calibration, the sensitivity, the minimum detectable field, and the frequency response are analyzed in detail. The system is highly sensitive, nonperturbing, and noninteractive. In addition to these advantages, the excellent property for measuring the phase of the RF magnetic field is experimentally confirmed by many field measurements. Resultantly, the minimum detectable RF magnetic field is obtained as 10 µA/cm (38 nW/cm² in power density) remarkably lower than others.